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Correct rotate_mask().

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This commit is contained in:
Thomas Harte 2022-04-10 09:31:39 -04:00
parent 140ae7a513
commit 284440336d
1 changed files with 10 additions and 4 deletions
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14
InstructionSets/PowerPC/Instruction.hpp
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@ -1446,11 +1446,17 @@ struct Instruction {
} }
/// Provides the mask described by 32-bit rotate operations. /// Provides the mask described by 32-bit rotate operations.
/// i.e. all bits from mb() to me() inclusive. ///
/// Per IBM's rules:
/// mb < me+1 => set [mb, me]
/// mb == me+1 => set all bits
/// mb > me+1 => complement of set [me+1, mb-1]
uint32_t rotate_mask() const { uint32_t rotate_mask() const {
const uint32_t mb_bit = 0x8000'0000 >> mb<uint32_t>(); const auto mb_bit = mb<uint32_t>();
const uint32_t me_bit = 0x8000'0000 >> mb<uint32_t>(); const auto me_bit = me<uint32_t>();
return mb_bit - me_bit + mb_bit;
uint32_t result = (0xffff'ffff >> mb_bit) ^ (0x7fff'ffff >> me_bit);
return result ^ ((mb_bit < me_bit+1) ? 0 : 0xffff'ffff);
} }
/// Condition register source bit A. /// Condition register source bit A.